This invention relates to television picture tubes, and is particularly concerned with the base of such tubes that provides for passing and isolating a number of electrically conductive pins that convey operating voltages into the tube envelope.
FIG. 1 depicts a representative base 10 which is attached to the terminus 11 of the narrow neck 12 of a cathode ray picture tube, the entirety of which is not shown. Neck 12 is terminated by a number of electrically conductive low-voltage pins 14, and at least one high-voltage pin 16; two such high voltage pins are shown in this example. As noted, pins 14 and 16 extend axially from the neck terminus 11. The potentials conducted by the low-voltage pins 14 may range from five volts to two kilovolts, while the potentials on the high-voltage pins 16 may range from four kilovolts to thirteen kilovolts. The resulting wide disparity in potentials between the closely spaced pins can lead to inter-pin arcing, the severity of which can damage television circuits and components and the associated electron gun in the tube neck. Also, such arcing can produce "arc tracks" on the base which, once established, can so degrade the high-voltage integrity of the base that the base must be replaced.
To provide for electrical isolation of the high-voltage pins 16 from the low-voltage pins 14, base 10 is shown as having a plurality of axially and radially outwardly extending insulating walls 18 which isolate the pins one from the other to prevent inter-pin arcing. The pins 16 which conduct a very high voltage may be further isolated from the low-voltage pins 14, and from each other, by an elaborate system of insulating walls and cavities. A base of this type which, in conjunction with a socket system, provides for high voltage arc prevention between adjacent pins is described and claimed in U.S. Pat. No. 4,075,531, assigned to the asignee of the present invention.
It is a common practice to supplement the insulation provided by the base by the addition of an electrically insulative material into a cavity 20 surrounding high-voltage pins 16. It will be seen that the cavity 20 opens onto terminus 11. The electrically insulative material is usually injected into the base 10 through an aperture 22 at the end of the base from the direction indicated by the arrow 24. The aperture 22 leads to an opening in the base 10 for receiving the hermetical seal tip of the tubulation (not shown) that extends from the terminus 11 of neck 12 following the tube evacuation and tip-sealing process. The insulative material 26, indicated graphically by dots, flows up into the opening in base 10 and into cavity 20 where it surrounds high-voltage pins 16. To ensure that the insulative material 26 completely fills cavity 20, a surplus of the material 26 is injected which exudes from the space between base 10 and neck terminus 11, as indicated graphically.
The insulative material 26 is also an adhesive which provides for adhering base 10 to neck terminus 11. The insulative material may comprise a thermo-setting polymer adhesive. The injection means is usually a hand-held, gun-type tool that utilizes air pressure to force the insulative material into the base.
The process of installing the base and injecting the insulative material during cathode ray picture tube manufacture is as follows: All pins are straightened so that the base 10 may be passed over the pins 14 and 16. The insulative material 26 is then injected by the means described. Any excess which exudes from between base 10 and neck terminus 11 is wiped off manually.
This seemingly simple process normally requires four production personnel: one to straighten the pins and install the base, one to inject the insulative material using the tool described, and two to wipe off the excess insulative material. Over three grams of the insulative material must be injected to ensure complete insulation of the high-voltage pins and positive adherence of the base to the neck terminus.